Are the research reactor generally safe due to their small size and inturnal features of sustainability?
Yes, there was Mol research reactor accident, which occurred in Belgium in 1965.
The link below & the provided reference will be useful.
Safety precautions are generally high & less size may lead to less danger but full care is required in all cases.
http://www.johnstonsarchive.net/nuclear/radevents/1965BELG1.html
In 1947, the 20 megawatt National Research Experimental (NRX) came online at the Chalk River facility. NRX was always the focus of the National Research Council’s Atomic Project. It was designed to be the workhorse of science and innovation. NRX was for a time the world’s most powerful research reactor, by the mid-1950s producing over 40 million watts of heat and vaulting Canada into the forefront of physics research.
On December 12, 1952, the NRX reactor underwent a violent power excursion that destroyed the core of the reactor, causing some fuel melting. Unaccountably, the shut-off rods failed to fully descend into the core. A series of hydrogen gas explosions (or steam explosions) hurled the four-ton gasholder dome four feet through the air where it jammed in the superstructure. Thousands of curies of fission products were released into the atmosphere, and a million gallons of radioactively contaminated water had to be pumped out of the basement and "disposed of" in shallow trenches not far from the Ottawa River. The core of the NRX reactor could not be decontaminated; it had to be buried as radioactive waste.
http://www.ccnr.org/paulson_legacy.html
https://en.wikipedia.org/wiki/Nuclear_and_radiation_accidents_and_incidents
http://www.nucleartourist.com/references/Descriptions%20of%20Selected%20Nuclear%20Reactor%20Accidents.pdf
description of selected accidents-----
Main accidents reported in nuclear research reactors:
1- Chalk River (1952) - Canada
The National Research Experimental (NRX) nuclear research reactor at Chalk River Laboratories experienced one of the world's major reactor accidents in December 1952, when the core of NRX reactor was damaged due to a meltdown caused by a power excursion and partial loss of coolant in the reactor.
The accident was classified under Level 5 on the INES. The reactor resumed operations within two years and operated until it shut down permanently in 1993. The facility is currently undergoing the process of decommissioning
2-Idaho National Engineering Laboratory (USA): 3 January 1961
A steam explosion in reactor SL-1 during preparation for start-up destroys the small US Army experiment23 September 1983
3-Centro Atomico Constituyentes (23.9.1983)
An operator at the RA-2 research reactor in Buenos Aires, Argentina received a fatal radiation dose of 3700 rad (37 Gy) while changing the fuel rod configuration with moderating water in the reactor. Two others were injured.
4- December 1991 A leak from pipelines in the vicinity of CIRUS and Dhruva research reactors at the Bhabha Atomic Research Centre (BARC) in Trombay, Maharashtra, India results in severe Cs-137 soil contamination of thousands of times the acceptable limit. Local vegetation was also found to be contaminated, though contract workers digging to the leaking pipeline were reportedly not tested for radiation exposure, despite the evidence of their high dose.
5-Date: 30 December 1965
Location: VENUS assembly, Mol, Belgium
Type of event: criticality accident with research reactor
Description:
The VENUS research reactor used uranium dixoide fuel rods containing 7% enriched uranium in a tank of water; at the time of the accident, 30% of the water was heavy water. During manipulation of control rods, an operator erroneously began extracting a control rod before reinserting another. The operator observed a glow in the bottom of the reactor, immediately dropped the control rod and left the room. His left foot, which was over the reactor at the time of the accident, absorbed 1750-4000 rem and had to be amputated; the dose to his chest was about 500 rem.
Consequences: 1 injury
Dear Yulia,
Please check with the IAEA's "Safety Reports Series No.53: Derivation of the Source Term and Analysis of the Radiological Consequences of Research Reactor Accidents.
APPENDIX I: PAST RESEARCH REACTOR ACCIDENTS from page 71
www-pub.iaea.org/MTCD/publications/PDF/Pub1308_web.pdf
Best regards,
Muharrem Keskin
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